The present invention relates in general to providing a power supply voltage, more particularly a DC voltage as power supply for an electronic circuitry, particularly as power supply for a portion of an integrated circuit.
Generally speaking, in battery-operated circuitry, such as for instance used in a mobile telephone, it is desirable that the energy consumption is as low as possible. For this reason, there is a tendency to design electronic circuitry, especially components of an integrated circuit, to operate at as low a voltage as possible. For instance, many of the components of an integrated circuit are able to operate with a supply voltage of 1.3 V. However, it may be that some of the components of an integrated circuit need a higher operating voltage, for instance 3 V, in order to operate correctly. For such circuitry, it is customary to provide a power source such as a battery for the lower supply voltage VDD1, and to derive the higher supply voltage VDD2 from the lower supply voltage VDD1 by means of a converter such as a DC/DC converter. However, it is also known to provide a power source such as a battery for the higher supply voltage, and to derive the lower supply voltage from the higher supply voltage by means of a voltage converter such as a DC/DC converter or a linear regulator. Hereinafter, the invention will be further explained for an illustrative example where the higher supply voltage VDD2 is derived from the lower supply voltage VDD1 by means of a DC/DC converter, but it will be understood that the invention is not limited to such embodiment.
The supply voltage for electronic circuitry needs to have a certain minimum value Vmin for the electronic circuitry to operate correctly. Such minimum value Vmin can be considered as a design characteristic of the circuitry. If the supply voltage to such circuitry would be higher than the minimum supply voltage Vmin, the circuitry would still operate correctly but with a less-than-optimum energy consumption. Therefore, it would be desirable if the output voltage VDD2 of the voltage converter would be constant and equal to Vmin. However, in practice the output voltage of a voltage converter is not constant but is controlled to fluctuate in a control range between a lower limit VLOW and an upper limit VHIGH. Herein, the lower limit VLOW is chosen to be approximately equal to the minimum supply voltage Vmin, whereas the difference VHIGHxe2x88x92VLOW is considered as a control margin. Thus, the converter in principle requires two operational parameters, i.e. VHIGH and VLOW In practice, VHIGH can be derived from VLOW by applying a fixed value xcex94V=VHIGHxe2x88x92VLOW; then, a converter needs only one input parameter VLOW. 
Conventionally, the boundaries of the control range of a converter are fixed. Then, in order to take into account possible manufacturing tolerances, VLOW should be chosen relatively high in comparison with Vmin. This implies a relatively high energy consumption for most applications.
In order to overcome this problem, according to an important aspect of the present invention, a voltage converter is controllable in that it comprises a parameter input for receiving an input signal that indicates a suitable value for the lower limit VLOW of the control range of the DC/DC converter, while further the voltage converter is adapted to control its output voltage VDD2, derived from an input voltage VDD1, to be at least equal to the lower limit VLOW as derived from the parameter signal received at said parameter input. Preferably, the parameter signal is a voltage level identical to VLOW. 
In contrast to Vmin, which is a design characteristic, VLOW is an operational parameter, which must be suitably set for achieving an acceptable balance between energy consumption and safety margin. If the value of VLOW would be chosen too high, the mean energy consumption of the integrated circuit would be undesirably high. On the other hand, if the value of VLOW would be lower than Vmin, the supply voltage to the integrated circuit might drop below Vmin, in which case the integrated circuitry would operate incorrectly or not at all.
A problem in this regard is that the exact, actual value of Vmin depends on, inter alia, the process xe2x80x9chistoryxe2x80x9d, i.e. the exact process conditions during manufacture of the voltage converter, so that the exact, actual value of Vmin may differ from one individual voltage converter to another. Further, Vmin is not constant but depends on, inter alia, the temperature of the integrated circuit. Therefore, it is desirable to have a parameter source for providing the control parameter VLOW for the voltage converter, which parameter source takes the above-mentioned dependency into consideration.
It is a further object of the present invention to provide such a parameter source.
According to an important aspect of the present invention, a parameter source for providing the control parameter VLOW is designed such that the characteristics of its output signal match substantially the characteristics of Vmin of the electronic circuitry. In a preferred embodiment, the parameter source comprises a voltage controlled oscillator (VCO) which is controlled to generate a constant frequency, wherein the VCO is implemented in the same chip as the said electronic circuitry, and wherein the control parameter VLOW is derived from the control voltage to the VCO. In a more preferred embodiment, said voltage controlled oscillator is incorporated in a phase locked loop (PLL) for controlling the VCO.
U.S. Pat. No. 5.359.300 discloses a PLL for use in a radio pager, wherein the function of the PLL is to generate frequencies for the pager. The components of the PLL operate on a first supply voltage VDD1, provided by a battery. One component of the PLL (more specifically: a charge pump of the PLL) is supplied with a second supply voltage VDD2. This second supply voltage VDD2 is derived from the battery voltage VDD1 by means of a DC/DC converter. Herein, the DC/DC converter only serves, as part of the PLL, to achieve a correct functioning of the PLL. The DC/DC converter comprises a switching transistor, which switches a booster coil, said switching transistor being controlled by a frequency signal that is derived from a frequency signal of the PLL. However, this publication does not disclose or suggest the concept of the present invention. More particularly, this publication does not mention the problem underlying the present invention, i.e. that an electronic circuitry needs to have a certain minimum supply voltage Vmin, nor does this publication provide a solution to this problem by disclosing a voltage converter which is controlled by a parameter signal indicating the lower limit VLOW of the control range of the converter.